My good friend IGL Coated my car and he said as long as you aren't washing your car in the baking sun...A lot of the soaps sold on the market are okay, he said he wouldn't recommend them, but in a pinch they'll work.
I take my car through the "Acid Baths" at the local Touch-Free car wash and it still looks as if he coated it yesterday.
Again, I'm not saying this is the proper way, but in a pinch, it's okay.